Abstract: The present invention is a process for the carbothermic reduction of silicon dioxide to form elemental silicon. Carbon balance of the process is assessed by measuring the amount of carbon monoxide evolved in offgas exiting the furnace. A ratio of the amount of carbon monoxide evolved and the amount of silicon dioxide added to the furnace is determined. Based on this ratio, the carbon balance of the furnace can be determined and carbon feed can be adjusted to maintain the furnace in carbon balance.

Abstract: The present invention is a process for smelting ferrosilicon alloy. The process comprises adding a carbon source and tailings comprising oxides of silicon and iron to a substantially closed furnace. Heat is supplied to the furnace by striking a direct current arc between a cathode electrode and an anode functional hearth. In a preferred embodiment of the present invention, the cathode electrode is hollow and feed to the substantially closed furnace is through the hollow electrode.

Abstract: The instant invention relates to the use of hollow silicon carbide beams as refractory in substantially closed open-arc furnaces used for the carbothermic reduction of metal oxides. The silicon carbide beams are used in areas of the furnace which are exposed to temperatures higher than those tolerated by standard refractories, said areas requiring, in addition, stability to oxidation and reduction type chemical reactions and sufficient electrical resistance to minimize arcing from the exposed electrode. In addition, the invention relates to the use of silicon carbide beams in a two-stage, open-arc furnace for the carbothermic reduction of silicon dioxide to silicon metal.

Abstract: The instant invention is a process for preparing silicon metal in a direct current, submerged-arc furnace. The process comprises adding a source of silicon dioxide and a source of carbon to a substantially closed furnace. Heat is provided to the furnace by striking a direct current arc between a moveable cathode and a anode functional hearth. Silicon metal is tapped from the furnace. The described process may also be used to prepare silicon metal alloys.

Abstract: A silicon smelting furnace and a process for utilizing this furnace for the production of silicon is described. The process involves a process in which equilmolar proportions of silicon carbide and silicon dioxide are charged to the reaction zone of a silicon furnace. Above the furance is placed a shaft containing particulate carbon in the amount of 2 moles of carbon per mole of silicon dioxide charged to the reaction zone. As energy is applied to the reaction zone, molten silicon, gaseous silicon monoxide, and gaseous carbon monoxide are formed, the gases passing through the shaft of carbon, converting the carbon to silicon carbide. The silicon carbide, so formed, is combined with an equimolar proportion of silicon dioxide, and the cycle is repeated. Aside from an initial charge of silicon carbide, the feeds to the smelting furnace are silicon dioxide and carbon, silicon carbide being formed concurrently in a bed of carbon separated from the furnace reaction zone during the smelting cycle.

Abstract: What is described is a process for the production of silicon via the carbothermic reduction of silicon dioxide in which silicon carbide is fed as the total reductant source or as a portion of the reductant input. The process also includes recovery and recycle to the furnace silicon monoxide and other silicon-containing materials from the by-produced gases from the furnace to maximize raw material efficiency. Finally, the process includes the recovery of value from the by-produced gases via the use of the gases as a chemical intermediate or the use of the gases as a fuel for a combustion process.

Abstract: What is disclosed is a method of improving the performance of the direct process for preparing alkylhalosilanes using an alkylhalide and silicon. The method is based on the control of the phosphorous that enters the silicon used in the direct process, by controlling the amount of phosphorous that enters the silicon during the manufacture of the silicon itself.

Abstract: The present invention relates to a process for the production of ferrosilicon in a closed two-stage reduction furnace. In the present invention, carbon monoxide released as a result of the smelting process, in the first stage of the furnace, is used to prereduce higher oxides of iron, for example Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, contained in a second stage of a furnace, to iron monoxide (FeO). The iron monoxide is then used as a feed material to the first stage of the furnace. The use of a closed furnace and a pre-reduction process results in substantial energy savings in the production of ferrosilicon alloy.

Abstract: A silicon smelting furnace and a process for utilizing this furnace for the production of silicon is described. The process involves a process in which equilmolar proportions of silicon carbide and silicon dioxide are charged to the reaction zone of a silicon furnace. Above the furnace is placed a shaft containing particulate carbon in the amount of 2 moles of carbon per mole of silicon dioxide charged to the reaction zone. As energy is applied to the reaction zone, molten silicon, gaseous silicon monoxide, and gaseous carbon monoxide are formed, the gases passing through the shaft of carbon, converting the carbon to silicon carbide. The silicon carbide, so formed, is combined with an equimolar proportion of silicon dioxide, and the cycle is repeated. Aside from an initial charge of silicon carbide, the feeds to the smelting furnace are silicon dioxide and carbon, silicon carbide being formed concurrently in a bed of carbon separated from the furnace reaction zone during the smelting cycle.

Abstract: What is described is an improvement to a process for the preparation of silicon from the reduction of silicon dioxide with a solid carbonaceous reducing agent, the improvement comprising feeding calcium compounds into the reaction zone of a silicon furnace, and controlling and maintaining a desired calcium level in the reaction zone of the silicon furnace. The calcium compounds may be fed to the silicon furnace as a constituent of either the silicon dioxide or solid carbonaceous reducing agent feeds, as a separate feed, or as a combination of two or more of these feeds.Also described is an improvement to a process for the preparation of silicon carbide from the reduction of silicon dioxide with a solid carbonaceous reducing agent.

Abstract: What is disclosed is an improvement in a process for the carbothermic reduction of silicon dioxide to form silicon, the improvement comprising (a) contacting the by-produced gases from the silicon furnace with a cooling medium such as a vaporizing liquified hydrocarbon-containing gas or an expanding compressed hydrocarbon-containing gas to cool the by-produced gases and to cause silicon-containing materials to completely condense and to form agglomerated solids; (b) removing the agglomerated, solid materials from the gases, and (c) recovering value from the solids-free by-produced gases as an energy source or as a chemical intermediate.

Abstract: What is disclosed is a process for preparing silicon using a gas plasma as a heat source. The process comprises (a) generating a gas plasma in a reactor utilizing a transferred arc plasma configuration in which a minimum of gas is utilized to form a plasma; (b) feeding silicon dioxide and a solid reducing agent directly into the reactor and to the plasma; (c) passing the plasma gas, the silicon dioxide, and the solid reducing agent into a reaction zone of the reactor; (d) recovering molten silicon and the gaseous by-products.

Abstract: Silica is reduced in a direct arc reactor by activated carbon or carbon black having relatively low boron (B) and phosphorus (P) contents to produce silicon having similarly low B and P contents and suitable for use in photovoltaic cells for converting solar energy directly to electrical energy.